Americans love the open road — it symbolizes the freedoms our country provides and a sense of exploration that has helped build our nation. The vast interstate network of asphalt and pavement for decades has facilitated people’s travel to places near and far for commerce or recreation. Now, that free system is under attack by some policymakers who want to roll back longstanding restrictions on tolling interstates. Doing that, as Massachusetts Transportation Department chief Richard A. Davey suggested in a July 25 Roll Call guest opinion column, would enable states to slap economically punitive fees on roads that traditionally have been toll-free. Such a policy reversal would be financially devastating for families and businesses, and the mere notion of it should alarm everyone who uses the interstates.

Supporters justify this strategy by claiming that new tolls can help replenish a dwindling federal Highway Trust Fund. Congress faces a tight deadline to raise new revenue for the nearly insolvent fund that has been in place since 1956 to help maintain a largely toll-free interstate system. There are many problems with tolling existing interstates. It is a publicly unpopular idea that is economically harmful to all who use the interstates, states have rejected this authority when it has been offered to them, and tolls can endanger public safety by diverting more vehicles onto local roads.

Fortunately, none of the leading temporary funding plans moving through Congress embrace President Barack Obama’s flawed tolling proposal to reinforce a highway fund that has been capitalized with gasoline tax revenue rather than relying on tolls. But that has not stopped pro-toll forces from making a public case for their misguided stance. In his Roll Call column, Davey argues “Congress should give states maximum flexibility to raise toll revenues from interstate highways.” What Mr. Davey’s advocacy ignores is the fact that no state has ever tolled existing lanes under the federal Interstate System Reconstruction and Rehabilitation Pilot Program of 1998, which gives three states an exception to federal tolling restrictions. None of them — Missouri, North Carolina and Virginia — have moved beyond preliminary authorization. Instead, lawmakers in all three have pursued legislative bans to prevent their interstates from being tolled. Those states have made it clear that this is a tool they don’t want, and they doubt that it would even work.

Davey highlights the key distinction in the toll debate, and inadvertently underscores the folly of tolling existing interstates, when he notes “Congress has allowed states to toll roads in limited circumstances, such as on new highways or high-occupancy toll lanes.” The linchpin in those “limited circumstances” is the provision of new capacity that must be paid for. Charging a toll in that scenario stands in stark contrast to tolling interstate lanes that have long been paid for by the driving public, especially when the option of toll-free lanes remains available. Making motorists pay new tolls on old lanes is double taxation, and it is fundamentally unfair because it can leave drivers without a toll-free alternative.

Beyond basic fairness, placing tolls on existing interstates is fiscally imprudent and can jeopardize public safety. Driving up travel costs on existing interstates raises costs for commuters and commercial transportation outfits. Both outcomes can wreak economic havoc on communities. Increased travel costs can strain family budgets and put a damper on routine purchases and travel, hurting stores and restaurants dependent on customer traffic. At the same time, rising freight expenses can take disposable income out of the economy because shoppers are paying higher prices at the register.

Another potential harm is diversion. Tolling existing lanes can divert passenger and commercial traffic onto local roads. Such a change in driver behavior can put more wear and tear on a secondary system less able to accommodate that load. In turn, that creates unanticipated road repair costs for local governments that taxpayers will ultimately shoulder. Diversion-related congestion can also imperil community wellbeing by delaying police, fire and rescue workers as they respond to life-threatening emergencies.

For all these reasons, it is clear that tolling existing interstates is not a viable funding mechanism. That is why Congress has wisely shown no interest in expanded state tolling authority even as it scrambles to generate scarce new road dollars with little to spare. For the sake of the open American road, we encourage Congress to stand fast in this conviction.

Julian Walker is the spokesman for the Alliance for Toll-Free Interstates.